Shown in FIG. 1 are portions of a centrifugal compressor 10 and annular-shaped combustor 12 of a gas turbine engine. The compressor 10 generally includes a rotating impeller 14 configured to accelerate and thereby increase the kinetic energy of the gas flowing therethrough. A stationary annular-shaped diffuser 16 circumscribes the impeller 14, and serves to decrease the velocity of fluid flow leaving the impeller 14 and thereby increase its static pressure. Diffusers are typically composed of either vanes or pipes that define a plurality of circumferentially-spaced passages 18. The cross-sectional area of each passage 18 typically increases downstream of the impeller 14 in order to diffuse the flow exiting the impeller 14.
Both vane and pipe-type diffusers generally include a transition region 20 downstream of the diffuser passages 18 to match the diffuser flowpath to the geometry of the combustor 12. As shown in FIG. 1, the transition region 20 includes an annular manifold 22 that receives the radially-outward air flow from the diffuser 16, and redirects this airflow aft and often radially inward (as shown) toward the annular-shaped entrance of the combustor 12. The manifold 22 terminates with a generally straight section 24 in which a number of deswirler vanes 26 are positioned immediately upstream of the entrance to the combustor 12. The vanes 26 serve to remove the residual circumferential swirl from the flow exiting the diffuser 16 by converting the high tangential velocity component of the flow exiting the diffuser passages 18 to a more useful static pressure. As a result, the flow exiting the deswirler vanes 26 and directed into the combustor 12 is characterized by relatively low swirl and Mach number and a particular meridional ("spouting") angle that together achieve more stable and efficient combustor performance. In a multistage centrifugal compressor, a diffuser and transition region may be used between each consecutive pair of stages to decelerate and deswirl the air flow exiting the leading stage to a level appropriate for the trailing stage.
The manifold 22 shown in FIG. 1 generally defines an axi-symmetric free bend that is bounded by one (outer) surface, though bends bounded by two (inner and outer) surfaces are also known. The deswirler vanes 26 within the straight section 24 that follows the bend within the manifold 22 are generally arranged on a conical axi-symmetric flow path. Though a single row of vanes 26 is shown, double-row configurations are known. As a rule, the vanes 26 have been placed downstream of the bend and immediately upstream or at the entrance of the combustor 12.
While diffuser and deswirler systems of the type shown in FIG. 1 perform well in a number of successful gas turbine engines, further improvements in the performance are continuously being sought. Of primary interest is achieving reductions in pressure losses that reduce engine performance.